Corrosion Control of Stainless Steels in Indoor Atmospheres—Laboratory Measurements Under MgCl₂ Deposits at Constant Relative Humidity (Part 1)

The susceptibility of stainless steel 316L (UNS S31603) to atmospheric induced stress corrosion cracking in conditions representative of the exposure to marine aerosols has been studied through laboratory tests on U-bend specimens. This study was performed to evaluate the durability of containers for the storage and disposal of intermediate-level radioactive waste during prolonged periods of exposure to atmospheric conditions in surface facilities. The results, however, are likely to be relevant to stainless steel components exposed to marine aerosols in cold and warm climates, particularly indoors (no direct solar irradiation). Tests were performed at constant tensile stress in the presence of MgCl₂, used to simulate seawater. Different temperature (i.e., room temperature of 50°C), relative humidity (about 30 and 60%) and chloride deposition density (10 μg cm⁻² to > 10,000 μg cm⁻²) were tested. The results show that atmospheric induced stress corrosion cracking tended to be significantly enhanced at higher temperatures and at relative humidity (RH) close to the deliquescence point of the salt (~30%), with cracks deep than 100 μm developing at a deposition density greater than 100 μg cm⁻². However, at room temperature or in conditions of higher relative humidity (60%), much higher deposition densities were required to observe any cracks.